1. Technical Field
The present invention relates to electronic compass systems and methods of operation therefor, and more particularly to a system and method for interpreting degree headings sensed by an electronic compass system in accordance with a plurality of predetermined degree ranges and displaying directional headings in accordance with the predetermined degree ranges.
2. Discussion
The present invention is related to and is an improvement of U.S. Pat. No. 4,622,843 to Hormel issued Nov. 18, 1986 entitled "Simplified Calibration Technique and Auto Ranging Circuit for an Electronic Compass Control Circuit". The present invention is also related to U.S. Pat. No. 4,807,462 issued Feb. 28, 1989, to Rafi A. Al-Attar and entitled "Method for Performing Automatic Calibrations in an Electronic Compass." These patents are hereby incorporated by reference. The present invention is related to and combinable with the commonly assigned patent application "Shifting System and Method for an Electronic Compass," application Ser. No. 07/815,267. This application is hereby incorporated by reference.
Normally, electronic compass systems employ a magnetic flux-gate sensor. The operation of the flux-gate sensor is well documented. See, Hisatsugu Itoh, "Magnetic Field Sensor and Its Application to Automobiles", SAE Paper No. 800123, pages 83-90, February, 1980; and Doug Garner, "A Magnetic Heading Reference for the Electro/Fluidic Autopilot," Sport Aviation, Part I, pages 19-26, November, 1981 and Part II, pages 20-32, 51, December, 1981. These documents are hereby incorporated by reference.
When an electronic compass system incorporating a flux-gate sensor is mounted to a vehicle, such as an automobile, it senses the earth's magnetic field as the vehicle travels, and also as the vehicle changes direction, and generates an output signal indicative of the heading of the vehicle. Typically, the heading is classified into one of eight headings corresponding to the geographic directions of North, Northeast, East, Southeast, South, Southwest, West and Northwest. Each geographic direction further typically comprises an equal range of 45 degrees. For example, the geographic North direction might typically be centered at 0.degree. on a compass rose, and would typically cover a range of about 337.5.degree. to 22.5.degree., or about .+-.22.5.degree. from the 0.degree. (due North) heading of the compass rose. Thus, the eight geographic directions typically are divided into perfectly equal ranges.
The above-mentioned division of the eight geographic directions into equal degree ranges is acceptable for some applications, such as marine navigation, where the vehicle, in such case a boat, is typically not confined to predetermined paths of travel such as roads. However, with motor vehicles such as automobiles, paths of travel are confined to roads, which in turn are most often laid out in accordance with the four major directional headings of North, South, East and West, or variations of these four directions. Roads that are marked and referred to as North-South or East-West running roads often include portions which vary from the markings of the road. For example, a North-South running road marked as "North" may meander at various points to become a slightly Northeast or Northwest heading road.
In situations such as described above, drivers of such vehicles can become confused when traveling on a "Northbound" road when an electronic compass system mounted on the driver's vehicle is indicating that the vehicle is traveling in a Northeast or Northwest direction. Since many, if not most North-South and East-West roads meander slightly from their overall directions at certain points, the chance for driver confusion can be significant. This problem can be particularly troubling when navigating freeways running through congested urban areas where such freeways, while traveling North-South or East-West overall, often meander considerably from their marked directions at various points.
Accordingly, it is a principal object of the present invention to provide an electronic compass system and method for interpreting degree heading signals from the system in a manner to help eliminate the confusion that exists when temporary variations are encountered in traveling primarily North-South and East-West roads, which are marked only as "North", "South", "East" or "West".
It is still a further object of the present invention to provide an electronic compass system and method of operation therefor which includes a controller and a look-up table, the look-up table having a plurality of predetermined degree ranges corresponding to the geographic directions of North, Northeast, East, Southeast, South, Southwest, West and Northwest, and wherein each of the predetermined degree ranges is uniquely associated with one of the just-mentioned geographic directions and wherein degree ranges of the major geographic directions of North, South, East and West are increased at the expense of the minor geographic directions of Northwest, Northeast, Southeast and Southwest.